Methods and apparatus for using large inertial body forces to identify, process and manufacture multicomponent bulk metallic glass forming alloys, and components fabricated therefrom

ABSTRACT

To identify and manufacture metallic glass forming alloys, large inertial forces or “g”-forces are created in a centrifuge assembly used to sequentially separate crystalline phases (particles) as they sequentially form and grow in a molten alloy during gradual cooling of the alloy below its liquidus temperature. These forces physically remove and isolate the actual crystalline particles from the remaining liquid as they are formed. Under the influence of a large g-force, this is accomplished by rapid and efficient sedimentation and stratification. Further contamination and nascent solid “debris” in the form of oxides, carbides, or other foreign particles can be removed from the molten alloy using the same sedimentation/stratification technique. Finally, a method of efficiently cooling and solidifying the final low melting stratified and decontaminated liquid into a solid glass component is proposed which utilizes convective heat transport by a cooling gas. The result is a vitrified bulk metallic glass component of near net shape.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/248,901, filed Nov. 14, 2000, and U.S. ProvisionalApplication No. 60/271,188, filed Feb. 23, 2001, the entirety of both ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a method and apparatus for theidentification and processing of bulk metallic glass forming alloys, andthe manufacture of components fabricated from these alloys.

[0004] 2. Description of the Related Art

[0005] During the past decade, numerous university and industrialresearch groups have invested significant efforts to discover metalalloy formulations which form glass when cooled from the molten state atrelatively slow rates of cooling. Vitrification or glass formation inmetal alloys was first discovered in about 1960 by P. Duwez andcoworkers at the California Institute of Technology (“Caltech”). Theyused “rapid solidification” techniques to produce glassy alloys bycooling the liquid alloy at rates of about 1 million degrees per second.A variety of such rapidly quenched metallic glasses were produced overthe following three decades.

[0006] Beginning in about 1990, the research groups of Prof. A. Inoue inJapan and Prof. W. L. Johnson at Caltech developed complex alloyscontaining 3, 4, 5 or more components which formed glasses at far lowercooling rates, typically 1-100 degrees per second when solidified fromthe equilibrium liquid state. During the past several years, these“bulk” glass forming alloys have attracted substantial commercialinterest as engineering materials. The bulk metallic glasses have highstrength, high hardness, high specific strength, and a variety of otheruseful engineering properties. Furthermore, the liquid alloys are highlyprocessable and can be cast into complex three dimensional very near netshapes. Interest in utilizing these materials in engineeringapplications has led to widespread interest in developing anddiscovering new bulk glass forming alloys, in processing these alloysfrom the melt, and utilizing these alloys to produce commercially usefulmaterials such as rods, plates, sheets, tubes, and other more complexshapes.

[0007] A key parameter which distinguishes alloys with exceptional glassforming ability is their relatively low melting point. Alloys which formbulk metallic glass undergo equilibrium melting of the initial alloyover a range of temperatures which are relatively low compared with thecompositionally averaged melting point of the pure metals which comprisethe alloy. Very often, the optimum glass forming alloy lies near aminimum in the melting surface (liquidus surface) of the alloy taken asa function of the alloy composition. This liquidus surface isconventionally represented in alloy phase diagrams as a “liquidusprojection.” For example, in a two component alloy, the liquidus curvecan be represented as a curve in the composition/temperature plane.

[0008] A simple example is shown in the Au—Si phase diagram of FIG. 1.This phase diagram of binary Au—Si alloy shows a eutectic composition 10with a eutectic temperature 12 of 363° C. The liquidus line 14represents the line above which a single liquid phase is present. Thesolidus line 16 represents the line below which the system hascompletely solidified. Note that the melting point of Au is about 1064°C. and that of Si is about 1414° C. Also illustrated is thecompositional partitioning of a slowly cooled liquid at an off-eutecticcomposition 18 during solidification where x_(L) is the composition ofthe remaining liquid.

[0009] In this simple binary case, the eutectic composition is preciselythe compositional range where Duwez and coworkers produced the firstmetallic glass by rapid quenching. More generally, low lying liquidustemperatures (e.g. near alloy eutectic compositions) locate the optimumglass forming regions in higher order ternary, quaternary, quinary, etc.glass forming alloys. See W. L. Johnson, 24 MATERIALS RESEARCH SOCIETYBULLETIN 42-56 (October 1999). Generally speaking, the ability to formmetallic glass is optimized at or near eutectic compositions, or moregenerally near the lowest lying temperatures of the liquidus surface internary, quaternary and higher order alloys. As such, the search foreasy glass forming alloys is very frequently found to be equivalent tofinding those alloy compositions corresponding to the lowest lyingmelting temperatures (or lowest lying liquidus surface). Most often, thebest glass forming alloys lie within about ±5 at. % of a minimum in theliquidus surface. The search for easy glass forming alloys is thusdramatically simplified when the lowest melting alloys can beidentified.

[0010] To locate glass forming compositions, it is critical to be ableto identify or “discover” alloys with chemical compositions located nearthe lowest lying regions of the melting curves in the higher orderalloys. Thus, it is of interest to develop an efficient means of bothdiscovering and isolating the lowest melting alloys in a complexmulticomponent alloys system containing two, preferably three or moremetals. In the case of alloys with more than three components, the phasediagrams are generally not available and little or no information existsto guide the researcher to the optimum low melting compositions.

[0011] It has actually been proposed to develop materials combinatorymethods whereby one searches for low melting alloys by literally makingthousands of alloy compositions (using for example thin film processingmethods) and screening their melting points in a rapid and parallelmanner. See 159 CHEM. WEEK 57 (1997). This approach requires carryingout literally thousands or tens of thousands of screening experiments.Thus, what is needed is a method of identifying the lowest melting alloyin a single or small number of experiments on a bulk liquid.

[0012] The production of bulk metallic glass, in addition to developinglow melting point alloys, also requires that the low melting liquidalloy be substantially free of contaminants, oxides, and debris whichinduce crystallization. For metals, the most frequently encounteredcontamination of the liquid is in the form of crystalline oxideparticles, carbide particles, and a variety of other types of nascentforeign substances. These contaminants are ubiquitous and ever presentin the processing of nearly all commercial metals used in casting ofmetallic components. In most common cases (e.g., casting of aluminum,iron, and titanium alloys), they are inevitable inclusions in theliquid. It is well known that this nascent contamination frequentlyinduces crystallization of the liquid alloy when it is undercooled belowits melting point. Metallurgists refer to this as heterogeneous crystalnucleation. Practically speaking, heterogeneous nucleation is extremelyharmful to the glass forming ability of metal alloys. As such, it wouldbe extremely desirable to develop methods to reduce or eliminate nascentoxide, carbide, and other debris from metallic melts when attempting toproduce metallic glass. Thus, what is needed is a direct and efficientmeans of removing most or nearly all of this nascent contamination anddebris from a molten alloy.

[0013] Finally, it is of importance to produce bulk metallic glass inuseful shapes. What is needed is a natural means of efficiently coolingand solidifying or casting a “decontaminated” alloy with an optimizedcomposition (having the lowest melting point) into plates, rods, tubes,or other very near net shape castings.

SUMMARY OF THE INVENTION

[0014] The preferred embodiments of the present invention address theseand other needs by providing a rapid and efficient method to identifyand physically isolate alloy compositions of low melting alloys whichreadily form bulk metallic glass. Certain preferred embodiments alsoprocess these materials in a manner which removes unwanted and harmfulimpurities and debris (such as crystalline oxide, carbide or nitrideparticles) in the molten alloy to improve the glass forming ability ofthe liquid alloy. Preferred embodiments also describe the production andmanufacture of large net shape castings, plates, rods, and other usefulshapes from the purified and compositionally optimized liquid alloy.

[0015] In one aspect of the present invention, a method of identifyingthe lowest melting eutectic composition of an alloy having “n” phases isprovided, where n ≧2. An arbitrary starting alloy is provided. The alloyis heated until it is substantially molten. Preferably, the molten alloyis subjected to an inertial force above its melting point for a periodof time. The temperature of the alloy is lowered while subjecting thealloy to a large inertial force or acceleration. An inertialacceleration is often also referred to as gravitational acceleration orsimply gravity where the gravity and acceleration have the oppositesense. The lowering of the temperature causes nucleation and growth ofcrystals of a first crystalline solid phase within surrounding liquid.

[0016] Crystals of the first solid phase are subjected a body orinertial force (preferably caused by inertial acceleration or gravity)such that the first solid phase moves either upward or downward (withrespect to the direction of the inertial acceleration) in the remainingliquid. As used herein, upward and downward (as well as top and bottom)do not necessarily refer to the ordinary meanings of these terms, butrather indicate direction with respect to the inertial acceleration,where bottom is opposite the direction of acceleration (or along thedirection of applied gravity). The direction of motion (i.e., upward ordownward) depends on the sign of the density difference between thecrystals and the surrounding liquid. Heavier crystals move opposite tothe direction of inertial acceleration; lighter crystals move along thedirection of the inertial acceleration. This process is commonlyreferred to as sedimentation.

[0017] Further lowering of the temperature of the alloy while subjectingthe alloy to said inertial acceleration and body forces causes furthernucleation and growth of additional solid phases, the additional solidphase crystals being subjected to the inertial forces such that theadditional solid phases move upward or downward, depending on the signof the difference in density between these crystals and the remainingliquid. Thus, as crystalline phases are sequentially formed, thecrystals sediment to the top or bottom of the liquid forming strata atthe top and bottom of the vessel which contains the liquid.

[0018] The temperature is further lowered until the alloy issubstantially completely solidified. The last solid phase to solidify isdesirably located between the previously solidified strata. However, itwill be appreciated that where the solid phases have substantially thesame density, the last solid phase to solidify does not necessarily haveto be between other previously solidified strata. The fmal liquid willhave the lowest melting point of all the solidified strata. In the casewhere this final liquid has a eutectic composition with a minimummelting temperature, the final liquid remaining will solidify at theeutectic composition in a well defined layer or strata. An alloy ofeutectic composition will be physically isolated in a well-definedlayer.

[0019] In another aspect of the present invention, a method of producinga bulk sample of a lowest melting eutectic composition of an alloy isprovided. An arbitrary starting alloy is provided. The temperature ofthe alloy is lowered while subjecting the alloy to an inertial force,the lowering of the temperature causing nucleation and growth of a firstsolid phase within surrounding liquid. The first solid phase issubjected to the inertial force such that the first solid phase movesupward or downward in the surrounding liquid. Further lowering of thetemperature of the alloy while subjecting the alloy to said force causesfurther nucleation and growth of additional solid phases, the additionalsolid phases being subjected to the inertial force such that theadditional solid phases move upward or downward. The temperature isfurther lowered until the alloy is substantially completely solidified.A bulk sample of alloy is then removed from the strata or layer whichwas the last to solidify. This lowest melting sample is then remeltedand cast in an effort to produce a bulk glass casting having thecomposition of this lowest melting alloy.

[0020] In another aspect of the present invention, a method ofprocessing a multicomponent alloy, comprising melting the alloy andsubsequently solidifying the alloy, both operations being carried out inthe presence of a centripetal acceleration field. In one embodiment, thealloy is solidified in the presence of an inertial acceleration or gfield of between about 1 and 10⁶ g's produced by centrifugal motion.Here, g is the acceleration of the Earth's gravitational field=9.8 m/s².

[0021] In another aspect of the present invention, a method of forming apurified, multicomponent bulk metallic glass forming alloy is provided.A sample alloy is melted at an elevated temperature. The molten alloy issubjected to a centripetal acceleration while holding it above themelting point for a period of time. The alloy is solidified by loweringthe temperature of the alloy while continuing to subject the alloy to acentripetal acceleration, the solidified alloy having a portionseparated from the remaining alloy having a lowest melting eutecticcomposition. The portion of the alloy having the lowest melting eutecticcomposition is isolated. The portion of the alloy having the lowestmelting eutectic composition is re-melted at an elevated temperaturewhile subjecting this portion to a centripetal acceleration. The portionof the alloy having the lowest melting eutectic composition is cooledwhile subjecting the portion to a centripetal field, the cooled alloyhaving a portion with relatively fewer impurities than the remainingalloy.

[0022] In another aspect of the present invention, a metallic alloyhaving a composition optimized for bulk glass forming ability isprovided. The composition is obtained by melting the alloy followed by aslow and gradual cooling and solidification of an initially molten alloyin a centrifuge. The centrifuge subjects the alloy to high inertialforces during solidification which physically separates crystallinephases from the remaining molten alloy, such that the optimizedcomposition of the metallic alloy is the last portion of the alloy tosolidify and is physically isolated in a well-defined layer of the finalalloy.

[0023] In another aspect of the present invention, a high temperaturecentrifugal processing device for processing molten metal alloys undervery high inertial accelerations is provided. A rotor is fabricated of ahigh temperature material having high strength and fracture resistanceat temperatures of between about 400 and 1200° C. and which is capableof withstanding inertial accelerations up to at least 50,000 g's. Aplurality of internal cavities within the rotor symmetrically laid outwithin the body of the rotor. A shaft onto which the rotor is mountedallows the rotor to be spun at high rotation frequencies of betweenabout 1000 and 100,000 rpm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a phase diagram of binary Au—Si alloy.

[0025]FIG. 2 is a schematic illustration of a solid spherical particlelocated in a liquid and falling in a centripetal g-field.

[0026]FIG. 3 is a schematic illustration of a centrifuge assembly fordetermining the lowest melting eutectic composition of a multicomponentalloy.

[0027]FIG. 4 is a phase diagram of the Fe—O system.

[0028] FIGS. 5A-5C are schematic illustrations of various rotor designsthat can be used in preferred centrifuge assemblies.

[0029]FIGS. 6A is a perspective view of a hermetically sealed capsuleused for containing a liquid alloy sample.

[0030]FIG. 6B is a cross-sectional view of a sample capsule having acrucible for containing a liquid alloy sample.

[0031]FIG. 7 is a cross-sectional view of a covered cavity design forloading sample capsules into a centrifuge assembly.

[0032]FIG. 8 is a cross-sectional view of a split rotor design forloading sample capsules into a centrifuge assembly.

[0033]FIG. 9 is a perspective view of a centrifuge assembly according toone preferred embodiment.

[0034]FIG. 10 is a perspective view of a rotor assembly used in thecentrifuge assembly of FIG. 9.

[0035]FIG. 11 is a perspective view of the rotor assembly of FIG. 10,shown open to illustrate the internal cavities.

[0036]FIG. 12 is an end view of the internal surface of one of theplates forming the rotor assembly of FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The preferred embodiments illustrated herein describe a methodfor identifying, processing and manufacturing a metallic glass formingalloy, and preferred apparatuses for accomplishing these methods. Moreparticularly, certain preferred embodiments describe the use of acentrifuge to create a centripetal force on a molten alloy as it iscooled in order to separate out the desired alloy composition and removeimpurities. It will be appreciated, however, that other methods anddevices may also be used to produce the desired separation. It will alsobe appreciated that the methods described herein may have applicabilityto beyond metallic glass forming alloys.

[0038] Stratification, Sedimentation and Fluid Mechanics

[0039] To accomplish the objectives outlined above, in one embodimentlarge inertial forces or “g”-forces are utilized to sequentiallyseparate crystalline phases (particles) as they sequentially form andgrow in a molten alloy during gradual cooling below the liquidustemperature. The crystalline particles are physically removed andisolated from the remaining liquid as they are formed. Under theinfluence of a large g-force, this is accomplished by rapid andefficient sedimentation and stratification. Further, contamination andnascent solid “debris” in the form of oxides, carbides, or other foreignparticles from the molten alloy can be removed using the samesedimentation/stratification technique. The resulting liquid is a finallow melting stratified and decontaminated liquid, which can beefficiently cooled and solidified into a solid glass component, such asby utilizing convective heat transport by a cooling gas. This results ina vitrified bulk metallic glass component of near net shape.

[0040] The large inertial or g-forces are preferably generated in oneembodiment by the rotational motion of a centrifuge. Using one of anumber of centrifuge designs, inertial acceleration a can be produced,for example ranging from about 1 to 10⁶ g's. Here g is the accelerationof gravity (9.8 m/s²). Using more advanced centrifuges, inertialacceleration of about 10⁵ to 10⁶ g's or more can be generated. Thisresults in a body force density ρ a per unit volume exerted on anyobject rotating with the centrifuge where ρ is the density of theobject. More particularly, a solid particle located in a liquid will besubjected to a net body force density given by:

f=(ρ_(s)−ρ_(L))a=Δρa

[0041] where ρ_(s)=density of the solid particle in kg/m³ andρ_(L)=density of the carrier liquid in kg/m³. For a solid particle ofvolume V, this results in a net body force of F=fΩ=ΔρaΩ. This well knownbody force causes the solid particle to move or sediment in the g-fieldand is responsible for the well known phenomena of sedimentation.

[0042] To illustrate, consider a solid particle in a liquid column asshown in FIG. 2. Assuming laminar flow, the drift velocity v of thesolid particle in the liquid can be calculated by knowing the viscosityof the liquid. For example, in the case of a simple spherical particle,this is given by equating the frictional drag on the particle to thebody force and is given by the following equation:

ΔρaΩ=3πμvd  (1)

[0043] or

v=[ΔρaΩ]/[3πμd]=[Δρad ²]/18μ  (2)

[0044] where d is the sphere diameter, Ω=(4π/3)(d/2)³=πd³/6, andμ=liquid viscosity measured in Pa-s. See R. CLIFT ET AL., BUBBLES,DROPS, AND PARTICLES 380 (Academic Press 1978). As an example, usinga=10⁴ g=10⁵ m/s², d=1 μm, Δρ=500 kg/m³=0.5 g/cc, and μ=0.01 pa-s, givesv=drift velocity=0.28 mm/s. The time required to sediment the particle adistance L will be τ=L/v. For L=10 cm, this requires about 300 secondsfor a 1 micron sphere to “sediment” a distance of 10 cm. Fornon-spherical particles such as an ellipsoid of non-unit aspect ratio,the time will be shorter.

[0045] Sedimentation Purification Rates/Time Scales

[0046] For a mixture of “heavy” solid particles in a less dense melt,geologists have shown that melt segregation along a centripetal forcefield over a column length L can be described by:

d[lnf]/dt=(l/f)df/dt=−v/L  (3)

[0047] where f is the volume fraction of solid phase, and v is theaverage drift velocity of a solid particle in a liquid in a g-field. SeeD. McKenzie, The Generation and Compaction of Partially Molten Rock, 25J. PETROL. 713-765.

[0048] In a simple approximation, the fraction of solid decreasesexponentially at the “top” of the column according to:

f=f ₀exp (−tv/L)=f ₀exp (−tΔρad ²/18 μL)  (4)

[0049] where the above expression (2) has been used for the driftvelocity v, and f₀ refers to the initial volume fraction of solidparticles.

[0050] The characteristic time scale for exponential decay of the solidvolume fraction at the top of the column is:

τ=[Δρad ²/18 μL] ⁻¹  (5)

[0051] If L=10 cm (as above) in a centripetal field of 10⁴ g, then τ=300seconds for a 1 μm particle with Δρ=0.5 g/cc, and μ=0.01 Pa-s=10centipoise. In the limit of initial volume fraction of particles, thismeans the concentration of particles decays by a factor of (1/e) in 300seconds, or a factor of 10 in about 700 seconds. For a particle ofdiameter 10 nm, the time scale for purification becomes 3×10⁶ seconds,or about 3 days. If L=1 cm, the same results are obtained for the 1 μmparticle in about 70 seconds (about 8 hours for the 10 nm particles).This is the characteristic time scale for melt purification with respectto 1 μm (10 nm) particles. This time scale is proportional to (1/d²), toμ=viscosity, to (1/a) where a=centripetal acceleration field, and to(1/L) where L =column length. This gives all of the essential physicsrequired to estimate temporal rates of melt purification in a two-phasemixture of liquid containing solid particles (assumed here to bespherical).

[0052] Ultimate Purification Levels

[0053] Turing now to the ultimate levels of “purification” that can beachieved in a centrifuge, quite generally, one can use the Lammdifferential equation to obtain transient and steady state solutions tothe problem of particle sedimentation in a centripetal field. See H.FUJITA, MATHEMATICAL THEORY OF SEDIMENTATION ANALYSIS (Academic Press1962). To obtain the ultimate steady state concentration profiles in acentripetal field, one can use the Archibald “steady state” solution ofthe Lamm equation. This is given by:

C(r)/C ₀=exp[sω ² r ²/2D]×[sω ²(R ₂ ² −R ₁ ²)/2D]/[exp(sω ² R ₂²/2D)−exp (sω ² R ₁ ²/2D)]  (6)

[0054] where C(r) is the particle concentration (particles/m³) at radiallocation r, C₀ the initial average particle concentration in the sample,s is the sedimentation coefficient of the particles, D is the diffusionconstant of the particles, r the radial coordinate of a centrifuge, andR₁ and R₂ the inner and outer ends, respectively, of a cylindricalsample vile located along the radial arm of the centrifuge rotating atfrequency of ω radians/s.

[0055] This steady state solution can be used to compute a steady statepartitioning (or “purification”) coefficient for the particles. This canbe defined as:

K=C(R ₁)/C(R ₂)=exp[sω²(R ₁ ² −R ₂ ²)/2D]  (7)

[0056] The Svedberg relation can be used to determine the ratio s/D. SeeFujita above. This is given by:

s/D=M(1−ρ_(I)/ρ_(s))/(k _(B) T)  (8)

[0057] where ρ_(L) and ρ_(s) are the respective densities of the carrierliquid and solid particle.

[0058] By way of illustration, the partitioning coefficient iscalculated for a typical case of a spherical solid particle with density10% greater than the carrier liquid assumed to have a typical value of5000 kg/m³. For particles with diameters of 1 μm and 10 nm (typicalcases of practical interest), M=2.6×10⁻¹⁵ and 2.6×10⁻²¹ kg,respectively. For k_(B)=1.38×10⁻²³ J/particle-K and T=1000 K (a typicaltemperature of interest), we have s/D=0.1 (M/k_(B)T)=19 and 1.9×10⁻²respectively. Applying equation (7) with R₁=0.4 m and R₂=0.5 m (a samplecolumn height of 10 cm), and ω=500 Hz, one obtains K=exp (2.14×10⁷) andexp (21.4)=2×10⁹. In the case of 1 μm spheres, purification isessentially complete while for 10 nm spherical solid particles,purification is 2 parts per billion. Accordingly, the method is capableof removing exceedingly small crystalline particles from the melt to alevel of parts per billion measured with respect to any initialconcentration of particles.

[0059] Use of a Centripetal Field during Liquid Alloy Solidification andCrystal Nucleation—Isolation of Lowest Melting Liquid in aMulticomponent Phase Diagrams.

[0060] To illustrate the application of the above principles indiscovery, isolation, and processing of bulk metallic glass formingalloys, several objectives of certain preferred embodiments are firststated. These are:

[0061] (1) Physical separation of the lowest melting eutectic alloy froman arbitrary starting alloy with the goal of “discovering” the lowestmelting alloy and physically isolating it.

[0062] (2) Elimination of solid crystalline debris or contamination(e.g. oxide particles) from the molten eutectic alloy to optimize glassforming ability.

[0063] (3) Production of a bulk metallic glass component from theisolated and purified” lowest melting or eutectic liquid.

[0064] To accomplish these goals, a liquid alloy in one embodiment issequentially melted and then gradually solidified by slow cooling in thepresence of a centripetal g-field. Preferably, this can be done with acentrifuge equipped with a high temperature furnace. FIG. 3 shows oneschematic illustration of the device. Further embodiments of centrifugaldevices are described below.

[0065] As shown in FIG. 3, the centrifuge assembly 20 is preferablyconfmed in a vacuum chamber 22. A rotor arm 24 rotates about a centralaxis 26, and twin furnaces 28 and 30 are provided within the arm 24 tocontrol the temperature in the chamber. The alloy samples are loaded insample holders, described below, which for the purposes of demonstrationcan be considered to be cylindrical. The sample holders are loaded intocavities 32 and 34 of the arm 24 adjacent each furnace. The assembly ispreferably instrumented with rotating high current contacts (not shown)to supply power to the resistively heated furnaces as well as lowcurrent rotating contacts for use in external measurements of thefurnace temperature using thermocouples.

[0066] As illustrated, ω is the angular frequency of the centrifuge, Ris the average radius of the furnace from the centrifuge point ofrotation. The acceleration at the furnace will be a=ω²R. For onepreferred device, a rotational frequency of about 5000 rpm, or about 80rotations/second, equals (2π)⁻¹ω, giving ω=500 radians/seconds For thisdevice, R=0.4 m, giving a=ω²R=2.5×10⁵×0.4 m/s²=10⁵ m/s²=10⁴ g.

[0067] Assuming that the temperature within the cylindrical sample canbe varied and maintained uniform (isothermal conditions) within thesample, an alloy having an arbitrary starting composition can beprocessed as follows. The alloy is first heated above its liquidustemperature until it is completely molten. The temperature is thengradually lowered stepwise until the alloy liquidus curve of the highestmelting crystalline phase in the equilibrium diagram is crossed. Thealloy is undercooled below this curve until the first crystalline phase(call it the α-phase) nucleates and grows. For the Au—Si system (FIG.1), at the initial composition shown, this first phase is nearly pure Sihaving the diamond cubic structure. Being less dense than the remainingliquid, these growing silicon crystals will be subjected to a g-force.For the case considered above, this g-force of about 10⁴ g's, will causerapid sedimentation to the interior of the centrifuge. If the growingcrystals reach only a size scale of about 10 nm, it will take a timescale of hours (note the large density differential Δρ for Au and Si inthis case) for sedimentation over a length scale of 10 cm.

[0068] The silicon crystals are rapidly and effectively moved to one endof the sample holder leaving the remaining liquid having the compositionof the liquidus curve at the temperature of interest. Upon furthercooling additional growth of existing silicon crystals along withfurther nucleation occurs. These crystals are in turn removed to theinnermost portion of the centrifuge (as they are less dense than theremaining liquid).

[0069] Finally one reaches the solidus curve at 363° C. (for the Au—Sisystem). Further undercooling ultimately produces nucleation and growthof Au in concert with Si (eutectic solidification). To the extent thatthe two phases solidify simultaneously by growth of the eutecticmicrostructure, further sedimentation and segregation is suppressed. Thelast portion of the sample to solidify will undergo eutecticcrystallization at a composition very close the eutectic composition inthe phase diagram. Following complete solidification, the sample iscooled to ambient temperature, the centrifuge brought to rest, and the“stratified alloy” removed from the centrifuge.

[0070] The sample can then be sectioned into slices perpendicular to theaxis of the original sample cylinder. The cross-sectioned slices arepreferably characterized by x-ray diffraction to identify phases and byan ion microprobe to determine overall compositions of the slices. Othermethods such as X-ray spectroscopy, EDS and Auger spectroscopy can alsobe used. The pure eutectic liquid will be located in the last “strata”which undergoes solidification. This “strata” will be characterized bythe presence of all phases (two phases, Au and Si in the example here)in one stratified section. This is the eutectic alloy.

[0071] The principle of the technique remains the same for the case ofthe ternary or quaternary eutectic alloys. If n is the order of thealloy (e.g. binary, ternary, etc.), then a eutectic point will becharacterized by the existence of n crystalline phases in equilibriumwith the liquid. Generally speaking, the strata which contains alln-phases will be the eutectic composition centrifugally segregated andsolidified alloy. By this method, one can physically isolate andidentify the eutectic composition in a higher order alloy by centrifugalprocessing of an arbitrary starting alloy provided only that thestarting alloy lies somewhere in the n-phase crystalline coexistenceregion in the low temperature phase diagram. In other words, thearbitrary starting alloy preferably includes n crystalline phases whenthe alloy is below the solidus temperature.

[0072] Purification of a Melt Containing Foreign Solid Particles Such asOxides

[0073] As case examples of melt purification with respect to oxides,considered below are representative examples of practical interest.There has been much effort devoted to synthesizing bulk metallic glassesbase on Fe. One of the most successful approaches to date has been touse a boron-oxide flux (B₂O₃) to suppress the effects of oxide particlesin inducing crystallization of glass forming Fe-based.

[0074] The problem can be understood by reference to the Fe—O binaryphase diagram shown in FIG. 4. The phase diagram shows a veryhigh-temperature liquid miscibility gap. At temperatures below 1500° C.,even iron alloys containing small levels of oxygen undergo liquid phaseseparation. Extrapolation of the miscibility gap to much lowertemperatures (less than 1000° C.) suggests phase separation of alloyscontaining oxygen in the tens of ppm range. Phase separation produces anoxygen rich melt containing roughly 50 at. % oxygen. This melt readilycrystallizes to the Wustite phase (a roughly equi-atomic oxide of iron).The Wustite phase in turn catalyzes nucleation of other crystallinephases (e.g. crystalline phases of Fe or other intermetallic phases inthe case of higher order alloys). The oxygen rich melt and the Wustiteparticles have substantially lower density (about 5.7 g/cc for theWustite phase) than liquid iron (about 7.2 g/cc). The difference isactually over 20% (by comparison with the 10% used in the illustrativecalculations above).

[0075] Both the oxygen rich melt as well as Wustite crystallites can beremoved from the remaining alloy (Fe-rich) by use of centrifugalseparation. The method is based on the sedimentation behavior describedabove. The alloy is slowly cooled step-wise from high temperature untilthe liquid miscibility gap is traversed. Phase separation produces anoxygen rich liquid phase (or Wustite crystal as the case may be) whichcan be removed by a g-force to a remote location from the remainingFe-rich melt. The primary requirements are that the oxygen rich phasescoarsen to a size in the 0.001 to 1 μm (or larger) range and that themelt be processed for time scales on the order of hours or days,depending upon the size of the particles and the exact time scales fromequation (5) above.

[0076] Under these circumstances, the remaining melt will be “purified”of oxygen rich liquid phase, of Wustite particulate debris, and ofheterogeneous nucleation sites for crystals. Removal of crystallineWustite particles down to nm sizes can be accomplished in time scales ofhours/days. The method can be applied to more complex Fe-based alloyscontaining a substantial fraction of Fe (typically greater than 70 at. %Fe). The principal of the method remains the same to remove oxygen richphases (both liquid and crystalline) from the remaining liquid alloy todecontaminate the melt of heterogeneous nucleation sites. This method isequally applicable to remove impurities, including but not limited tooxide and carbide particles, from alloys other than Fe alloys. Theseimpurities are not nominally intended to be present in the alloy butarise from the lack of purity of materials from which the alloy is made.

[0077] Casting of a Bulk Metallic Glass Component

[0078] Once a metallic alloy has been identified and/or purified usingthe methods described above, casting of metallic glass components frompurified low melting liquids can be carried out in at least one of twogeneral ways. These can be referred to as “ex-situ” and “in-situ”casting, as described below.

[0079] Ex-situ Casting. In one embodiment the alloy can be solidifiedentirely in the centrifuge following the initial processing steps of (1)isolating the low melting eutectic composition, and (2) purifying thislow melting alloy of crystalline debris (oxides, carbides, etc.) whichacts to catalyze heterogeneous crystal nucleation. The isolated/purifiedmelt is cooled by shutting down the power to the furnaces on thecentrifuge while maintaining rotation. The centrifuge itself is shutdown once the solidified alloy has been cooled to ambient temperature.The cooling of the alloy to ambient temperature preferably occurs at arate sufficient to suppress crystallization of the alloy. Thus, thepurified eutectic or low melting alloy that is removed from thecentrifuge is preferably an amorphous metal, and can be used as a feedstock for a traditional casting process.

[0080] In-situ Casting. The purified and isolated low melting pointalloy can be directly cast into a net shape component. In this case, acasting gate is preferably provided at the appropriate location in thesample column. This location is situated at a position on the columnwhere the purified eutectic melt is located. In practice, the lowmelting or eutectic alloy is first identified by a series of initialcentripetal experiments aimed at isolating and identifying the lowestmelting alloy as described above. An alloy of this nominal compositionis then used as feedstock for the centripetal casting. The optimizedfeedstock material is melted in the centripetal furnace. It is thenpurified of any oxide or other crystalline debris (using the abovemethods). A gate is provided which carries the melt to a metal mold ordie from a location in the melt column which is far removed from regionswhere the crystallize debris has sedimented. The melt that is removedthrough the gate preferably is transferred to the mold or die whilestill at or near its eutectic temperature. Once in the mold, the alloycan be cooled at a rate sufficient to suppress crystallization, therebyforming an amorphous metallic alloy.

[0081] The above descriptions outline the features of the generalapproach to be used. Additional details regarding casting of amorphousmetallic alloys are described in U.S. Pat. No. 5,950,704, U.S. Pat. No.5,711,363, and U.S. application Ser. No. 09/879,545, filed Jun. 11,2001, the entirety of each of which is hereby incorporated by reference.

[0082] Components cast using the methods above preferably can be made inbulk (e.g., having a smallest dimension exceeding about 1 mm). Thecomponents preferably have a glassy or amorphous structure which wasproduced using the centripetal processing method either by the “in-situ”or “ex-situ” casting methods described above. A “bulk” cast componentcan also be made having a partially amorphous or glassy structure. Morepreferably, one embodiment of a bulk cast component has at least 20volume % amorphous phase in its microstructure. Preferred embodimentsalso describe the production and manufacture of large net shapecastings, plates, rods, and other useful shapes from the purified andcompositionally optimized liquid alloy.

[0083] Preferred Centrifuge Devices

[0084] As discussed above, a method for identifying and processingmetallic glass forming alloys and fabricating components thereof usinglarge inertial forces to process liquid metal alloys at hightemperatures (in the molten state) has been provided. This method ispreferably implemented using a centrifugal processing platform. Theimplementation of the method preferably uses acceleration or g-forces.Here, an acceleration of 1 g is the acceleration of earth's gravity (9.8m/s²). Accelerations ranging from about 10³ g (9.8×10³ m/s²) up tovalues as high as about 1 mega-g or about 10⁶ g in the processing ofliquid metal alloys are preferred.

[0085] To implement this method, a device preferably includes: (1) acentrifugal device/platform capable of generating and sustaininginertial accelerations up to the mega-g range (10⁵-10⁶ g's); (2) acentrifugal device capable of holding or containing both a solid orliquid metal alloy sample on the centrifugal platform during rotation;(3) the capability to heat the metal alloy sample to temperatures aboveits melting temperature while subjecting the molten alloy to largeinertial accelerations (mega -g) for sustained periods of time(preferably from tens of seconds up to tens of hours); and (4) thecapability to control the environment in which the molten alloy isprocessed. Specifically, to implement the method optimally, one needs toprocess the molten metal in either a vacuum on a controlled gasatmosphere. As such, the liquid alloy should be situated in a controlledvacuum or gas atmosphere environment during processing at high gaccelerations.

[0086] The actual temperature requirement (3) will depend upon themelting temperature of the alloy in question. In certain preferredembodiments, commercially useful structural metals such as aluminum,titanium, iron, nickel, copper, etc. can be used. The typical range ofmelting temperatures will fall between about 400° C. up to about 1200°C.

[0087] For requirement (4), the entire apparatus is preferably locatedin a hermetically sealed container, or the alloy samples areencapsulated in a hermetically sealed container which can be mounted onthe centrifuge and which can remain sealed when subjected to hightemperatures and large inertial accelerations (up to the mega-g range).

[0088] To the inventor's knowledge, there are no commercially availablecentrifuges or centrifugal devices which support all of theserequirements. Requirement (3) is particularly challenging as thecombination of high temperature and large inertial forces will challengethe mechanical integrity of the rotating centrifugal platform (hereuponcalled the rotor).

[0089] To overcome these difficulties, a high temperature centrifugaldevice is provided which offers the capability of processing highmelting point liquids under mega-g range (about 10⁻⁵-10⁶ g)accelerations for extended times in a controlled environment.

[0090] High Temperature Rotor

[0091] The proposed device can be realized in several ways. Anexemplifying realization comprises a rotor constructed of a suitablehigh temperature material. Here, a high temperature material is amaterial which maintains a suitable level of strength, resistance todeformation, and resistance to fracture and failure at an elevatedtemperature when subjected to the high stress loads associated withmega-g range accelerations. Examples of suitable rotor materialsinclude, but are not limited to, high temperature steels such as Inconelalloys; Ni-based super-alloys (such as used for rotating jet enginecomponents); toughened high temperature ceramics, such as alumina,zirconia, magnesia or yttria; and vitreous or pyrolytic carbon.

[0092] All of these materials are known to have significant strength andtoughness at elevated temperatures. For example, Inconel alloys can haveyield strengths of about 500 MPa at temperatures as high as 900° C.Vitreous carbon, or glassy carbon rods, crucibles, and components areknown to have failure strength as high as 600 MPa at temperaturesranging up to 1500° C. A monolithic rotor is preferably fabricated fromone of these high temperature materials.

[0093] Preferred rotors will be fabricated of a high temperaturematerial having high strength and fracture resistance at temperatures ofabout 400-1200° C. which is capable of withstanding inertialaccelerations up to at least 100,000 g's. These rotors can preferably bespun at high rotation frequencies of about 1000 to 100,000 rpm. In oneembodiment, the rotor is capable of withstanding accelerations up toabout 50,000 g's at the rotor perimeter, more preferably up to about100,000 g's, and even more preferably up to about 250,000 g's.

[0094] Simple illustrations of preferred rotor components are shown inFIGS. 5A-5C. FIG. 5A illustrates a disk rotor 36 mounted on a shaft 38.FIG. 5B illustrates a rod rotor 42 mounted on a shaft 44. FIG. 5Cillustrates a hub rotor 48 having a plurality of blades 52 mounted on acentral hub 50 rotating about a shaft 54. In each of these embodiments,the rotor is a monolithic fixture of symmetrical shape which is balancedin order to spin at high frequencies on a shaft without vibration. Thisis a common requirement for all preferred centrifuges.

[0095] The rotors of FIGS. 5A-5C each contain internal cavities forholding a sample alloy. The cavities are laid out within the rotor in asymmetric arrangement. For example, four cavities 40 are shown in FIG.5A, two cavities 46 are shown in FIG. 5B, and four cavities 56 are shownin FIG. 5C. It will be appreciated that 2, 3, 4, 5, 6, 8, or any othernumbers of cavities in a symmetrical arrangement could be used. Thenumber of cavities to be used will depend on the overall mechanical loadrequirements to which the overall rotor will be subjected.

[0096] The presence of the cavities will reduce the maximum load that torotor can withstand and thus reduce the maximum rotation frequency therotor can support. As such, the cavities should generally be relatively“small”. For example, if the rotor is as shown in FIGS. 5A-5C and has aradius R and thickness t (normal to the page), and the cavities arecylindrical with diameter d and length L, then D/t is preferably small,more preferably less than about 0.5. L/R is also preferably small, morepreferably less than about 0.6, in order to maintain sufficientmechanical integrity of the rotor under the stress load imparted byrotation.

[0097] When the rotor is in the shape of a rod such as in FIG. 5B, therotor may have a circular, circular, square, rectangular, or othershaped cross section. The rod 42 is preferably spun about a shaft 44oriented normal to the principal (long) axis of the rod and located atcenter of the rod. The rod 42 preferably contains two internal cavities46 located between the shaft and the ends of the rod. The rod/cavityassembly can be spun about the shaft at elevated temperatures(preferably about 400-1200° C.) whereby the ends of the rod sustaininertial accelerations of at least 50,000 g and preferably up to about250,000 g or more.

[0098] The rotor of FIG. 5C preferably has blade-like protrusions 52extending from a central hub. Each protrusion contains a sampleprocessing cavity 56. This rotor is preferably shaped for optimizationof the maximum attainable inertial accelerations.

[0099] The rotors of FIGS. 5A-5C preferably span a length of betweenabout 10 cm to about 3 meters. In other words, this length correspondsto the diameter of the disk in FIG. 5A or the length of the rod in FIG.5B.

[0100] Sealed Sample Capsules and Crucibles

[0101] The cavities of FIGS. 5A-5C are used to accommodate samples to beprocessed. The samples themselves are preferably housed withinhermetically sealed capsules 58, such as shown in FIGS. 6A and 6B. Theliquid alloy sample 60 to be processed is preferably contained eitherdirectly in the capsule 58, or in a crucible 62 housed within thecapsule such as shown in FIG. 6B. The liquid alloy sample 60 is sealedwithin the capsule 58 either under vacuum or under an inert gasatmosphere. The capsule 58 may contain the alloy sample directly (nocrucible) provided that the reactivity of the subject sample in themolten state with the capsule material is not severe so as to eithercontaminate the sample or degrade the mechanical integrity of thehermetically sealed capsule (e.g. failure of the capsule hermetic seal).

[0102] When reactivity is of concern, a suitable crucible should be usedto contain the alloy. The crucible can be made from a variety ofsuitable materials, including but not limited to fused silica, vitreouscarbon, a refractory metal or ceramic material such as alumina orzirconia. In one preferred embodiment, the crucible 62 can be made ofmanganese.

[0103] The hermetically sealed sample capsule is preferably made of amaterial which can support large inertial stresses (typically about10-500 MPa) at elevated temperatures (about 500-1500° C.) and should besuitable for convenient hermetic sealing of the crucible and alloysample under either vacuum or inert gas. Examples of a suitable capsuleinclude, but are not limited to an Inconel or high temperature steelcapsule which can be sealed by welding caps onto a cylindrical cruciblein a controlled environment (for example e-beam welding under vacuum orinert gas), a silica capsule which could be vacuum sealed by glassblowing, a Ni-based super alloy, and a refractory metal such asmolybdenum.

[0104] A convenient means of loading the sample capsules into the rotorcavities is preferably provided. For this purpose, various rotor designscan be employed. An example of a covered cavity design is shown in FIG.7. The centrifuge assembly 64 shown in FIG. 7 preferably includes arotor 66 which can be designed in accordance with the embodiments ofFIGS. 5A-5C, or other embodiments, and a drive shaft 68. The sample 60(not shown) is loaded into a sample cavity 70 lying just beneath theupper surface of the rotor 66, and a cavity cover 72 is releasablyfastened to the rotor 66 to seal the cavity.

[0105] Another example of a suitable rotor cavity design is shown inFIG. 8. Here a split rotor design is provided to give access for loadingsample capsules. The assembly 74 includes a rotor split along thehorizontal plane into two plates 76 and 78, and a rotor drive shaft 80.Sample cavities 82 are disposed in the surfaces of the components whichface each other. Fasteners 84 are preferably used to seal the componentstogether.

[0106] It will be appreciated that the embodiments of FIGS. 7 and 8 aremerely two possible configurations for providing access for loadingsamples into a rotor cavity and are not intended as complete list ofpossible configurations. In evaluating the merits of variousconfigurations, the mechanical integrity of the rotor should be takeninto account. Both of the above configuration provide reasonabledesigns. Further embodiments are described below.

[0107] Method of Heating Rotor and Control of Rotor Temperature

[0108] To implement the centrifugal processing method, a means ispreferably provided to heat the entire rotor assembly containing thesample capsules. Various methods can be employed. In one embodiment,similar to the testing of rotating aircraft components at elevatedtemperatures characteristics of component service, rotating componentsare “spin tested” in a furnace. In this method the entire rotor andshaft assembly are inserted into the furnace and heated to the ambienttemperature of the furnace. Ni-based super-alloy and Inconel componentsare routinely tested to temperatures of up to about 1000° C. using thismethod.

[0109] In preferred embodiments, the rotor containing cavities andsample capsules can be inserted into a furnace. In contrast, one canalso raise a cylindrical furnace up over the rotor The furnace can bepreheated or heated following insertion of the rotor. In either case,the entire rotor assembly will ultimately be heated to the steady statetemperature inside the furnace. Using this method, the rotor assembly isheated to temperatures sufficient to melt the sample alloys inside thecapsules. As the sample capsules are essentially enclosed in a blackbodycavity, the sample temperature will rapidly equilibrate to the rotortemperature. The rotor and samples can be spun up to maximum rotationfrequency of the rotor and the samples processed under high inertialaccelerations.

[0110] Using an Inconel or super-alloy rotor, calculations show thataccelerations of about 1 to 2 times 10⁵ g can be achieved attemperatures up to about 1000° C. The rotor can then be removed from thefurnace or the power to the furnace can be reduced to provide gradualcooling of the rotor and encapsulated samples. Thus, solidification canbe carried out during the continued application of the high gacceleration.

[0111] As an alternative to the above method, the rotor can be heated byproviding a heating source for the rotor. For example, the rotor can beheated while spinning using RF induction heating. Here, RF coils wouldbe used in a configuration surrounding the rotor. When driven by an RFpower supply, the RF coils couple to the metal rotor and RF power iscoupled directly to the rotor. By adjusting the intensity of the RFpower, one can achieve varying “steady state” rotor temperatures. Thismethod can be readily implemented to heat an electrically conductingrotor to temperatures ranging to 1200° C. or higher where heat loss fromthe rotor is primarily by radiation. For a metal rotor of high thermalconductivity, the rotor will achieve a relatively uniform temperature insteady state. Likewise, the samples encapsulated within the rotor willachieve near isothermal conditions as required for processing liquidalloys at a well defined temperature.

[0112] Other methods in addition to inductive heating and resistiveheating can be used to heat the rotor assembly. Alternatively, one couldutilize a laser to heat the rotor assembly. Here, relatively highpowered laser would be required. Other heating methods include directresistive heating of the rotor. In this case, a high current rotatingelectrical feed-through would be required to bring current from anexternal power supply into the rotating rotor assembly. All of the aboveheating methods can be used to implement the preferred embodiments ofthis invention.

[0113] For processing liquid metal alloys, it will also be desirable toknow the temperature of the samples (e.g. the rotor) as a function oftime and acceleration history in order to control the processing of theliquid metal under high g acceleration. To measure the temperature ofthe rotor during processing, several methods can be employed. Theseinclude the use of an infrared or optical pyrometer to externallymonitor the rotor temperature during processing, and the use of one ormore calibrated thermocouples mounted on the rotor with junctionslocated within the sample cavities, preferably in direct contact withthe samples. To utilize thermocouples, a rotating electrical connectionis preferably used to feed the thermocouple signals to an externalvoltmeter or monitoring system. Either of the above methods would beeffective for monitoring the sample temperature history during high gprocessing.

[0114] Experimental Results

[0115]FIG. 9 illustrates one preferred centrifuge assembly 100 that canbe used to process glass forming metallic alloys. The assembly 100includes a cylindrical body 102 enclosing a chamber 104, and a lid 106provided over the body 102 for sealing the chamber. The cylindrical body102 preferably acts as a furnace to control the temperature inside thechamber 104, and is capable of producing temperatures of up to about1600° F. (about 875° C.) while the rotor (described below) is spun atrotation frequencies up to about 35,000 rpm, more preferably up to 1200°C. The body 102 and the lid 104 are preferably made from a suitablesteel or ceramic material which can withstand the high temperatureswithout degradation. The sample chamber preferably has an internaldiameter of about 30-60 cm.

[0116] Extending through the lid 106 of the furnace is a drive shaft108. The drive shaft is constructed of a high temperature creepresistant alloy such as Waspalloy or Inconel 100. A rotor 110, describedin further detail with respect to FIGS. 10-12, is provided at the bottomof the shaft. Thus, when the lid 106 is closed over the cylindrical body102, the rotor 110 is provided inside the chamber 104.

[0117] As shown in FIGS. 10-12, the rotor 110 is comprised of twoadjacent plates 112 and 114. As shown in FIGS. 11 and 12, the internalsurfaces of each of these plates contains a plurality of recesses 120for housing sample capsules such as described above. When the two platesare closed together, the recesses together define internal cavities forholding the sample capsules. As shown in FIGS. 11 and 12, eight cavitiesare provided in the rotor, although any number of cavities could beused. As shown in FIG. 10, the upper and lower plates of the rotor 110are held together using fasteners 116 which extend through openings 118in the plates.

[0118] The rotor is preferably made of a material which maintains anelevated strength (preferably greater than about 500 MPa) at elevatedtemperatures (preferably up to about 900° C. or higher) and resistscreep under load at such temperatures. One preferred rotor isconstructed from Inconel 100, although any of a number of materials suchas described above can also be used. A Ni-based superalloy, or apyrolytic carbon/carbon-fiber reinforced material would also be suitablefor construction of the rotor. Other rotor components including thefasteners, sample capsules (contained within the rotor cavities) canalso be fabricated from Inconel 100.

[0119] The overall disk shaped rotor (containing the sample cavities) inone embodiment has a preferred diameter in the range of about 10 cm to50 cm. In one preferred embodiment, the rotor has a diameter of about 25cm. The thickness of the rotor disk is preferably between about 1 cm and5 cm, more preferably about 2 to 3 cm. The cavities within the rotorpreferably each have a length of about 2 to 10 cm, more preferably about5 cm, and a diameter of about 0.5 to 2 cm, more preferably about 1.27cm. The rotor is preferably capable of accelerations up to about 60,000g (600,000 m/s²), more preferably up to about 200,000 g (2,000,000m/s²). One preferred device was tested at accelerations up to 120,000 g(at the outer end of the sample cavities). Cooling times of about 1minute to 10 hours may be used, more preferably with cooling rates ofabout 0.001° C./second to about 10° C./second.

[0120] It should be understood that certain variations and modificationsof this invention will suggest themselves to one of ordinary skill inthe art. The scope of the present invention is not to be limited by theillustrations or the foregoing descriptions thereof, but rather solelyby the appended claims.

What is claimed is:
 1. A high temperature centrifugal processing devicefor processing molten metal alloys under very high inertialaccelerations, comprising: a rotor fabricated of a high temperaturematerial having high strength and fracture resistance at temperatures ofbetween about 400 and 1200° C. and which is capable of withstandinginertial accelerations up to at least 50,000 g's; a plurality ofinternal cavities within the rotor symmetrically laid out within thebody of the rotor; and a shaft onto which the rotor is mounted whichallows the rotor to be spun at high rotation frequencies of betweenabout 1000 and 100,000 rpm.
 2. The device of claim 1, wherein the rotorcomprises two internal cavities.
 3. The device of claim 1, wherein therotor comprises four internal cavities.
 4. The device of claim 1,wherein the rotor comprises eight internal cavities.
 5. The device ofclaim 1, wherein the cavities extend to an upper surface of the rotorand are each sealable with a cover.
 6. The device of claim 1, whereinthe rotor is enclosed within a high temperature furnace.
 7. The deviceof claim 1, wherein the rotor is heated using an element selected fromthe group consisting of an external induction heating coil, an externallaser, and a resistive heating element mounted on the rotor itself tocouple heat to the rotor.
 8. The device of claim 1, further comprisinghermetically sealed sample capsules within said internal cavities. 9.The device of claim 8, wherein the sample capsules are made of asuitable high temperature material which can withstand high temperaturesof between about 400 and 1200° C. and concurrent high g accelerations upto 250,000 g's without failure of the hermetic seal.
 10. The device ofclaim 8, wherein the sample capsules are fabricated from a materialselected from the group consisting of high temperature steel, Inconel, aNi-based super-alloy, molybenum and a refractory metal.
 11. The deviceof claim 8, wherein the sample capsules include crucibles therein. 12.The device of claim 11, wherein the crucibles are fabricated from amaterial selected from the group consisting of refractory metal, aceramic, vitreous carbon and fused silica.
 13. The device of claim 1,wherein the rotor can withstand inertial accelerations up to about100,000 g's.
 14. The device of claim 1, wherein the rotor can withstandinertial accelerations up to about 250,000 g's.
 15. The device of claim1, wherein the rotor is a long rod including two internal cavities. 16.The device of claim 1, wherein the rotor is made from a materialselected from the group consisting of Inconel, a high temperature steel,a Ni-based superalloy, vitreous carbon, ceramics, alumina, zirconia,magnesia and yttria.
 17. The device of claim 1, wherein the rotorcomprises a plurality of blade-like protrusions.
 18. The device of claim1, wherein the rotor spans a length of between about 10 cm to 3 meters.19. The device of claim 1, further comprising thermocouples to monitorthe temperature of the rotor.